Specific genetic programs are activated by a network of multiple transcription factors during development resulting in tissue and/or stage specificity in their function and expression. A major objective of this ongoing study is to elucidate the molecular mechanisms underlying intestine specific expression using sucrase-isomaltase (SI) as a model gene. Cdx1 and Cdx2 were shown to be key factors in the transcriptional regulation of a number of intestine specific genes. We have shown that Cdx1 and Cdx2 proteins transactivate a number of intestinal specific gene promoters including SI, IPAL, and lactase, and regulate cell growth and intestinal differentiation in cultured cells. However, the pattern of expression of the SI gene in enterocytes does not correspond to the expression of Cdx1 and Cdx2, suggesting they are necessary but not sufficient to drive the correct pattern of SI gene expression. We present new data that Cdx2 is a phosphorylated and acetylated protein and transcriptional activity of Cdx2 is enhanced by forming a complex with hepatocyte nuclear factor 1 (HNF1), GATA factors, and coactivators such as CBP and PCAF. This current grant proposal is based on the hypothesis that Cdx1 and Cdx2 functions are modulated by post-translational modifications including phosphorylation and acetylation, and these alter SI gene transcription activity via chromatin modifications. This hypothesis will be pursued through the following interrelated, focused Specific Aims: Aim 1. To characterize phosphorylation sites in Cdx1 and Cdx2 and examine cellular signaling pathways that regulate Cdx phosphorylation. Aim 2. To elucidate the functional role of Cdx2 phosphorylation in vivo. Aim 3. To characterize acetylation of the Cdx2 protein and study the functional role on transcriptional activity of Cdx2 in vivo and in vitro. Orchestrated regulation of functional activities of Cdx1 and Cdx2 is significant, since they play a role in cellular differentiation and proliferation. Therefore, an understanding of the regulatory process of the Cdx proteins on intestine gene expression will provide new insights into normal intestine development as well as abnormal development which occurs in intestinal neoplasia and a framework of intestinal development and differentiation will emerge and come to fruition.